Definition of Secondary Hypertension
Secondary hypertension is defined as high blood pressure caused by an identifiable and potentially correctable underlying condition or disease, present in approximately 10% of adult patients with hypertension. 1
Key Characteristics
Secondary hypertension differs from primary (essential) hypertension in several important ways:
- It has a specific identifiable cause (unlike primary hypertension where the cause is unknown)
- The underlying condition may be potentially treatable or even curable
- It accounts for approximately 5-10% of all hypertension cases in adults 1, 2
- In children, secondary causes are more common, especially in those younger than 6 years 3
Common Causes of Secondary Hypertension
The most frequent causes include:
- Obstructive sleep apnea (most prevalent secondary cause, present in up to 83% of patients with resistant hypertension) 4
- Primary aldosteronism (present in approximately 20% of resistant hypertension cases) 4
- Renovascular disease (renal artery stenosis)
- Renal parenchymal disease
- Drug and substance use (NSAIDs, oral contraceptives, corticosteroids, decongestants, anticancer drugs, cocaine, amphetamines) 4
- Endocrine disorders (pheochromocytoma, Cushing syndrome, thyroid and parathyroid conditions)
- Congenital conditions (coarctation of aorta, congenital adrenal hyperplasia) 1
Clinical Features Suggesting Secondary Hypertension
Certain clinical features should prompt evaluation for secondary causes:
- Onset of hypertension before age 20 or after age 50 5
- Sudden worsening of previously controlled hypertension
- Malignant hypertension with end-organ damage (BP ≥180/110 mmHg with acute hypertension-mediated organ damage) 4
- Resistant hypertension (requiring more than 3 medications from different classes) 5
- Specific physical findings (abdominal bruits, sudden rise in creatinine with ACE inhibitors) 4, 5
- Unprovoked hypokalemia (suggesting primary aldosteronism or renovascular disease) 5
- Characteristic body habitus (truncal obesity, purple striae in Cushing's syndrome) 5
Diagnostic Approach
The European Heart Journal recommends the following diagnostic tests for suspected secondary hypertension 4:
| Suspected Cause | Recommended Screening Test |
|---|---|
| Primary aldosteronism | Aldosterone-to-renin ratio |
| Renovascular hypertension | Renal Doppler ultrasound, CT/MR angiography |
| Pheochromocytoma | 24h urinary/plasma metanephrines and normetanephrines |
| Obstructive sleep apnea | Overnight polysomnography |
| Renal parenchymal disease | Renal ultrasound, urinalysis, eGFR |
| Cushing's syndrome | 24h urinary free cortisol, dexamethasone suppression |
| Thyroid disease | TSH |
| Hyperparathyroidism | PTH, calcium, phosphate |
| Coarctation of aorta | Echocardiogram, CT angiogram |
Clinical Significance
Early recognition of secondary hypertension is important because:
- It can lead to more effective, targeted treatment approaches 1
- Some causes may be potentially curable with specific interventions
- Untreated secondary causes can lead to accelerated target organ damage 2
- Even with treatment of the underlying cause, blood pressure may not return to normal due to vascular remodeling, highlighting the importance of early detection 2
Management Principles
Management involves treating the underlying condition, which may include:
- Primary aldosteronism: Unilateral adrenalectomy for unilateral disease or mineralocorticoid receptor antagonists for bilateral disease 4
- Renovascular disease: Renal angioplasty for fibromuscular dysplasia; optimal cardiovascular risk management with consideration of stenting for atherosclerotic disease 4
- Obstructive sleep apnea: Weight loss, CPAP therapy, mandibular advancement devices 4
- Pheochromocytoma: Surgical removal after adequate alpha-blockade (alpha-blockers must be initiated before beta-blockers) 4
- Medication-induced: Discontinuation or substitution of causative agents when possible
Important Clinical Considerations
- Despite treatment of the underlying cause, hypertension may persist due to concomitant essential hypertension or irreversible vascular changes 2
- Ambulatory blood pressure monitoring is essential to rule out white-coat hypertension and confirm true resistant hypertension 4
- In children, secondary causes are significantly more common in those younger than 6 years, while 85-95% of hypertension in adolescents is primary 3
- Referral to specialists (endocrinology, nephrology, vascular surgery) should be considered for complex cases 4